CVE-2022-50145

In the Linux kernel, the following vulnerability has been resolved:

dmaengine: sf-pdma: Add multithread support for a DMA channel

When we get a DMA channel and try to use it in multiple threads it

will cause oops and hanging the system.

% echo 64 > /sys/module/dmatest/parameters/threads_per_chan

% echo 10000 > /sys/module/dmatest/parameters/iterations

% echo 1 > /sys/module/dmatest/parameters/run

[ 89.480664] Unable to handle kernel NULL pointer dereference at virtual

address 00000000000000a0

[ 89.488725] Oops [#1]

[ 89.494708] CPU: 2 PID: 1008 Comm: dma0chan0-copy0 Not tainted

5.17.0-rc5

[ 89.509385] epc : vchan_find_desc+0x32/0x46

[ 89.513553] ra : sf_pdma_tx_status+0xca/0xd6

This happens because of data race. Each thread rewrite channels's

descriptor as soon as device_prep_dma_memcpy() is called. It leads to the

situation when the driver thinks that it uses right descriptor that

actually is freed or substituted for other one.

With current fixes a descriptor changes its value only when it has

been used. A new descriptor is acquired from vc->desc_issued queue that

is already filled with descriptors that are ready to be sent. Threads

have no direct access to DMA channel descriptor. Now it is just possible

to queue a descriptor for further processing.